In dentistry, a unit for acquiring dental radiographic images is known comprising an X-ray head for emitting X-rays; at least one supporting arm supporting the X-ray head; and connecting means connecting the X-ray head to the supporting arm.
The connecting means normally comprise a connecting bracket hinged to the X-ray head and the supporting arm by two cylindrical joints to rotate, with respect to the X-ray head and the supporting arm, about respective hinge axes substantially crosswise to each other.
Each cylindrical joint comprises a hub; and a pin fitted in rotary manner in, and connected frictionally to, the hub.
Known units for acquiring dental radiographic images of the above type have various drawbacks, mainly due to the friction connection of the pins to the relative hubs, which, on the one hand, makes the X-ray head fairly hard to move about the hinge axes, and, on the other, once the X-ray head is set to the correct position, fails to ensure the correct position is maintained.